The gasification process converts biomass (feedstock) into a synthetic combustible gas primarily comprising carbon monoxide and hydrogen with some methane and other organic gasses. The basic process is relatively simple: the feedstock is exposed to a relative high temperature in an oxygen starved environment such that complete combustion of the feedstock does not occur. The process is not truly combustion in that the feedstock is only partially oxidized to yield the combustible fuel gas. Simple gasification technologies differ, and in view of the present invention, only technology focusing on biomass as a feedstock (to the exclusion of coal and petroleum based materials) are considered, except as rubber may be considered as a source of fine particulate material.
U.S. Pat. No. 5,178,076 issued Jan. 12, 1993 to Hand, et al. and entitled, “Biomass Burner Construction,” and U.S. Pat. No. 5,284,103, a division of the '076 patent issued February 8, to hand characterize the basic biomass burner in their specifications. The described burners comprise two “burning chambers,” are typically “up-draft for air flow, and place great emphasis on an air flow grate at the base of the first burning chamber and a spent fuel system to remove gasification by products.
U.S. Pat. No. 5,922,092 issued Jul. 13, 1999 to Taylor discloses a bottom feed, up-draft gasification system. The system comprises four major elements: a thermal reactor similar in function to the '076 and '103 patents, within fuel gas conveyed to a mechanical cleaner, thence to a cooler, and finally to an electrostatic precipitator. With respect to prior art, the system of the '092 patent overcomes in part certain problems of cleaning and cooling the fuel gas produced.
In U.S. Pat. No. 6,647,903 issued Nov. 3, 2003, discloses both a process to produce by gasification a combustible fuel gas with reduced tar content and a device (gasifier) specifically adapted for application of the described method. The device depends on specific internal geometry and on specific points of introducing air to control processing temperature, thereby controlling tar production and accumulation.
U.S. Pat. No. 6,808,543 issued Oct. 26, 2004 to Paisley reflects improvements in a alternative type of gasifier. The '543 patent discloses and claims both improved methods and an apparatus for operating a parallel entrainment fluidized bed gasifier system. The improvement involved addition of MgO to biomass to reduce agglomeration and a device to facilitate the flow of sand and char between gasifier compartments and minimize the flow of gasses between the compartments. Sand is used as the medium of heat exchange.
U.S. Pat. No. 6,871,603 issued Mar. 29, 2005 to Maxwel includes a plurality of claims for a gasifier system. The system comprises, generally, a gasifier, a site for preparing biomass for gasification, a boiler for combusting fuel from the gasifier to produce “useful energy,” and air delivery system to serve the gasifier, and a fan system to maintain the boiler and gasifier under negative pressure. The preparation site presses excess moisture from the biomass and utilizes air drying for additional moisture reduction. The gasifier is a bottom fed, up-draft facility with a blower to deliver air to intake inlets with dampers to control air flow. Combustible fuel is conveyed from the gasifier to the boiler where it is mixed with air and combusted to yield useful energy.
In U.S. Pat. No. 6,960,234 issued Nov. 1, 2005, Hassett discloses and claims in detail a multifaceted gasifier and related method. The gasifier is designed with a fixed-bed gasification element for processing relatively coarse biomass fuel material and an entrained gasification element wherein pulverized, liquid or solid, or gaseous biomass materials are processed to yield a combustible fuel gas produced by gasification driven by the fixed bed gasification element.
U.S. Pat. No. 6,981,455 issued Jan. 3, 2006 to Lefcort embodies technology to convert wet biomass to a useful, combustible fuel, utilizing a two-stage wet gasifier. The first stage gasifier chamber comprises sets of vertical and horizontally aligned bars to (i) support the waste material to be gasified and remove by-product ash and (ii) supply combustion air.
U.S. Pat. No. 7,007,616 issued Mar. 7, 2006 to Abrams and Cuilvey describes and claims a biomass gasifier system wherein biomass is conveyed to a gasifier chamber via fire belts, and oxygen input is metered along the length of each belt to control the temperature in the gasification chamber. Carbon dioxide is introduced as an oxygen diluent for the input oxygen. Oxygen is separated from ambient air by a (pressure) air separation unit. The combustible fuel gas produced by the gasification process is combusted in association with a boiler to produce useful energy.
Many process that combust a variety of materials, including biomass, yield by-products that are recognized as significant air pollutants, including as is widely recognized, particulate matter that comprises a significant part of smoke. Many of these particulate materials also have the potential to yield useful, combustible fuel when gasified. In U.S. Pat. No. 6,261,090 issued Jul. 17, 2001, Bosewell et al. describe and claim technology uniquely directed to the gasification of smoke, or combustion by-products.
Thus, there remains room for improvement in integrated biomass converter systems related to converting raw biomass material to yield an unprocessed fuel that can be gasified to yield a combustible fuel gas and systems wherein the energy potential of the biomass fuel can be adjusted by introduction of hydrogen and/or oxygen with or without simultaneous introduction of fine particulate matter and also by the addition of other, specific types of organic and inorganic wastes, and further wherein the energy potential of the combustible fuel can be adjusted by the addition of hydrogen or oxygen.